This article is about a mythological figure. For the software, see Aegir (software); for the tidal bore on the English River Trent see River Trent.

Aegir, originally Ægir, is considered the ruler of the sea in Norse mythology. He is a personification of the power of the ocean and its strength for good or ill in the affairs of men. In Norse poetry, the "jaws of Aegir" were what sank ships at sea. He was also known for throwing massive parties for the gods.

Snorri in Skaldskaparmal identifies Aegir with Gymir and Hlér who lived on Hlesey. Gymir, it may be noticed, is the name of the monstruous and terrible giant of the underworld, the father of the beautiful Gerd wooed by Freyr. Hymir, who seems to be a sea-giant, has a link with the gods, for he is said in Hymiskviða to be father of Tyr.

Aegir is said to have had nine daughters with his wife, Ran. His daughters were called the billow maidens. They were named (Bara, Blodughadda, Bylgia, Dufa, Hefring, Himinglaeva, Hronn, Kolga, and Unn). The names of each reflect the types of waves of the sea; they wore white robes and veils. (cf. his counterpart Poseidon)

Aegir is son of Fornjót and brother of Logi 'fire, flame' and Kári (wind). He is also called Hlér and Gymir. In the Lokasenna, he has a festival for the gods, where he provides the ale brewed in an enormous pot provided by Thor. The story of Thor getting the pot for the brewing is told in the Hymiskviða.

Aegir had two servants, Fimafeng (killed by Loki) and Eldir.

Other spellings

• Common Swedish form: Ägir
• Common Danish form: Ægir
• Also known as: Gýmir